Atomizing nozzle for producing a spray from a liquid under pressure

ABSTRACT

A method and device are described for atomising liquids, in which the liquid is forced through an annular gap formed between a spherical or conical surface and a circumambient hole in a plate, which components may be displaced relative to one another to control the flow of liquid through the gap. The size of the gap is controlled by a stop.

This is a continuation of application Ser. No. 07/905,240, filed Jun.26, 1992, now abandoned.

FIELD OF THE INVENTION

The invention relates to atomizing nozzles commonly used for, but notlimited to, hand held sprayers such as so-called aerosols and pump typeatomisers, intended for the application of liquid household, cosmeticand pharmaceutical products.

BACKGROUND OF THE INVENTION

Aerosol type sprayers are used throughout the world for dispensing awide range of products, for example hair lacquer, furniture polish,cleaners, paint, insect killers and medicaments. Until recently,chlorofluorocarbons (CFC's) were the most common of the propellant gasesused in aerosols because they are inert, miscible with a wide range ofproducts, are easily liquefied under low pressures, give a substantiallyconstant product flow-rate, and can produce sprays of droplets havingmean diameters in the range of 3 to over 100 micrometers. However, inthe 1970's it was confirmed that CFC's were probably responsible fordepleting the Earth's protective ozone layer, and in 1987, mostcountries signed the Montreal Protocol to phase out the use of CFC's.Alternative propellants were then introduced--for example liquefiedhydrocarbon gases such as butane, and carbon dioxide, which is dissolvedin the product, --but these are flammable or otherwise harmful to theenvironment, or react with the product, and these propellant gases aregradually being phased out. There has been much development of aerosolspowered by compressed gas (e.g. nitrogen, air), and manually operatedpump atomizers, and for the majority of applications the performance ofsuch sprayers is adequate.

The main drawback of these non-CFC sprayers is that the smallest sizeddroplet that can be produced is about 40 micrometers diameter, anddespite considerable development of so-called mechanical breakupnozzles, the use of high pressure (circa 15 bars) pumps, and lowviscosity/surface tension product formulations, 40 micrometers appearsto be the lower limit achievable with prior art methods and devices.

There are aerosol generators used for research and hospitalapplications, such as ultrasonic nebulisers and spinning discgenerators, but neither is suitable for portable, convenient atomizers.

It is also possible to force liquid at high pressure through a verysmall hole (5-10 micrometers diameter) to produce droplets of about 5micrometers diameter, but these methods are unsuitable or uneconomic forlarge scale manufacture, mainly because of the difficulty in making verysmall holes in a suitable material, and, to prevent blockage of thehole, the need for exceptional cleanliness in the manufacture of theparts, together with ultrafiltration of the fluid to be sprayed.

For veterinary and some human vaccination applications, high pressure(125-500 bars) spring or gas operated pumps (so-called needle-lessinjectors) are in common use to inject a jet of drug through the skin("intra-dermal injection") without the use of needles, and attachmentsare available to convert the jet to a spray for administering drugs tothe nasal passages of large animals such as swine. However, the smallestdroplet size obtainable is in the order of 40 micrometers, and the rangeof applications for these injectors is limited.

Compressed air atomizers such as air brushes and commercial paintsprayers consume large quantities of air, and to obtain droplets of 5micrometers with water for example, a gas to liquid ratio of over30,000:1 is required, which is impractical for convenient, portablesprayers.

Nevertheless, there are some applications that rely on a smaller dropletsize for maximum efficacy: space sprays such as flying insect killersshould contain droplets ideally in the range of 20-30 micrometersdiameter to ensure a long flotation time in the air, and for metereddose inhalers (MDI's) used for treating certain respiratory disorders itis essential that the aerodynamic particle size should be less than 15micrometers, preferably less than 5 micrometers, so that the dropletsare able to penetrate and deposit in the tracheobronchial and alveolarregions of the lung. For a spray composed of droplets with a range ofsizes, more than 5% by weight of the droplets should have an aerodynamicsize less than 6.4 micrometers, preferably more than 20 by weight of theparticles have an aerodynamic size less than 6.4 micrometers.

Inhalers may also be designed to deliver drugs to the alveolar sacs ofthe lung to provide a route for adsorption into the blood stream ofdrugs that are poorly adsorbed from the alimentary tract. To reach thealveoli it is essential that the aerodynamic size of the particles isless than 10 micrometers, preferably 0.5-5 micrometers.

Many of the drugs used in the treatment of respiratory disorders areinsoluble in vehicles such as water and are dispensed as suspensions.The drugs are produced in a respirable size of 1-5 micrometers.Particles of this size tend to block the very small holes (5-10micrometers) used by known devices to generate droplets of about 5micrometers diameter.

SUMMARY OF THE INVENTION

The present invention aims to provide a design of atomizing nozzle whichis capable, inter alia, of being used to give a nozzle which willproduce a spray of droplets of a size suitable for inhalation, withoutthe use of liquefied gas propellants. However, the present invention isbelieved to be capable of being used to give a nozzle which will producea spray of droplets having a mean diameter anywhere in the range of from0.5 to over 100 micrometers.

According to the present invention there is provided an atomizing nozzlefor producing a spray of droplets form a liquid passing through thenozzle under pressure, which nozzle comprises means defining an orifice;a closure member for the orifice, the orifice-defining means and closuremember being relatively movable with respect to one another between afirst position in which the closure member cooperates with the orificeto close it and a second position in which the closure member is spacedfrom the orifice-defining means to define a gap therebetween; and a stopfor limiting relative movement between the orifice-defining means andthe closure member to ensure that the width of the gap cannot exceedthat which will produce a fine spray.

Although the invention is intended mainly for metered dose inhalers andmanually operated pumps, it may also be applied in other applicationsrequiring small droplets, for example in certain industrial processes.

In one embodiment of the present invention the nozzle has a circularorifice which is sealingly closed by a ball urged by a spring. Under theaction of liquid under pressure, the ball is displaced from the orificeby an amount determined by the stop, which may be fixed or adjustable,and the fluid flows through the gap thus formed and emerges as a thincircular sheet. As the sheet of liquid expands it becomes thinner, andthe outer edge breaks into droplets, the diameters of which aredetermined by the size of the gap, the pressure of liquid, and thephysical properties of the liquid. When the pressure in the liquid isreduced below a predetermined level, the ball is urged by the springsealingly onto the orifice, thus preventing ingress of dirt, evaporationof the product, and atmospheric contamination.

In another embodiment of the invention, the liquid to be sprayed iscaused to flow past a spherical surface and through a gap formed betweenthat surface and a circumambient hole in a plate. The plate ispreferably made of a spring material and located so that it is insealing contact with the spherical surface as a normally closed valve.Under the action of liquid under pressure, the plate is forced away fromthe spherical surface by an amount determined by the stop, which may befixed or adjustable, and the fluid flows through the gap thus formed toemerge as a thin circular sheet. As the sheet of liquid expands, itbecomes thinner, and the outer edge breaks into droplets, the diameterof which are determined by the size of the gap, the pressure of liquidand the physical properties of the liquid. When the pressure in theliquid is reduced below a predetermined level, the spring plate returnsto its original position to seal against the spherical surface, thuspreventing ingress of dirt, evaporation of the remaining product, andatmospheric contamination.

Whilst reference has been made above to the use of a ball or sphericalsurface in co-operation with a circular orifice in a plate or nozzle,other shapes could be used, for example, a conical surface co-operatingwith a circular hole. The precise profile of the surface and hole willbe determined in part by the spray pattern required, and the presentinvention provides for all combinations of surfaces and holes, but it ispreferred that at least one of the components has a varying crosssection so that the gap between them is opened or closed as a result ofrelative movement. Since the stop ensures that the gap is ofsubstantially constant size when the components are fully apart, an evenspray results from the passage of fluid throughout the length of thegap. The width of the gap is preferably of the order of 5 micrometers.The ratio of the length of the gap L to the width of the gap D ispreferably not more than 1 and more preferably not more than 0.5. By the"length" of the gap we mean the distance which the liquid has to travelin order to pass through the gap.

The surface finish of the co-operating components in the region of thegap should be sufficiently fine so as not to adversely affect thedroplet size and pattern of the spray: for example, a groove in onecomponent would cause a stream of liquid to issue therefrom, which wouldprobably not have the required characteristics, and could lower thepressure in the liquid sufficiently to adversely affect the quality ofspray emerging from the remainder of the gap. The finish should besufficiently fine to ensure efficient sealing between the componentswhen in the closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates the principle of the invention and is a crosssectional view of the basic elements in their normal, non-pressurisedrelationship.

FIG. 2 is a similar view to FIG. 1, and shows the elements in theoperating position.

FIGS. 3 and 4 show a modified form of the embodiment of FIGS. 1 and 2.

FIGS. 5 and 6 show an alternative embodiment of the principle of theinvention, in closed and open position respectively.

FIG. 7 is an enlarged part section showing the conjunction if theprincipal components illustrated in FIGS. 5 and 6.

FIG. 8 shows a section through a modified version of the spring plateused in the embodiment FIGS. 5 and 6.

FIGS. 9 and 10 show a modified form of the embodiment of FIGS. 5 and 6.

FIGS. 11 and 12 show a spray device for use as an inhaler, incorporatinga nozzle according to the present invention.

FIG. 13 shows the nozzle used in FIGS. 11 and 12, on a larger scale.

FIG. 14 shows another form of spray device incorporating; the nozzleaccording to the invention.

FIG. 15 shows an embodiment of the nozzle having a gap of adjustablesize.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, ball 1 is resiliently urged by a compression spring6 into a position in which it is sealingly located on the circularorifice 3 of nozzle 2. Stop means 5 is located on the longitudinal axisof the ball and orifice, and has a gap 8 between the face 9 of the stopmeans 5 and the surface of ball 1. Nozzle 2 is in hydrauliccommunication with a dispensing means (not shown) and contains liquid 7which is to be sprayed.

Referring now to FIG. 2, which illustrates the same components as inFIG. 1, pressure has been applied to the liquid 7 by the dispensingmeans, and ball 1 is lifted from the circular orifice 3 against theforce of spring 6 until it stops against the face 9 of stop means 5.Thus the ball 1 has moved by an amount controlled by the gap 8 to form agap 10, the size of which is less than gap 8 by an amount determined bythe ratio of the diameters of the ball 1 and circular orifice 3. Theliquid 7 issues through the gap 10 as a circular sheet of thicknessinitially determined by the size of gap 10. As the liquid sheet expandsit becomes thinner, until the surface tension of the liquid is unable tomaintain homogeneity of the sheet, and the periphery of the sheet breaksinto small droplets. The size of the droplets is controlled by thedimension of the gap 10 and the velocity of the liquid, which in turndepends on the pressure generated in the dispenser. A smaller gap 10will generally produce smaller droplets, provided that the pressure inthe liquid is sufficiently high to overcome the viscous drag created bythe small gap, and accelerate the liquid to form a thin sheet. (If thepressure is too low, the liquid will merely ooze from the gap).

When the pressure in the liquid 7 ceases, the ball 1 is returned tosealing contact with orifice 3 by spring 6. It is preferable that thecontact line between the ball 1 and orifice 3 is very thin, which may befacilitated by chamfering the nozzle as at 4, so as to leave a knifeedge. This may have the additional effect of allowing a wider sprayangle Z than possible with a square-edged orifice. The orifice 3 has achamfered peripheral surface with the direction of chamfering being suchas to reduce the length of the gap between the ball 1 (closure member)and the nozzle 2 (orifice-defining means).

FIGS. 3 and 4 show a modification in which the stop means 5 is replacedby an alternative stop means 5a which has a recess 5b within which thespring 6 is housed. When the nozzle goes from the closed position shownin FIG. 3 to the open position shown in FIG. 4, the ball 1 seats itselfin the open end of the recess. The guidance which this provides ensuresthat the ball is correctly aligned with respect to the end of theconduit 2, with a uniform annular gap between the orifice 3 and theball. The spray produced is thus substantially uniform both indistribution around the gap and in droplet size.

An alternative embodiment is shown in FIGS. 5 and 6. In this case, FIG.5 shows a spherical surface 20 which is located at the outer edge of thedischarge conduit 21 containing the liquid to be sprayed 22. A springplate 24 having a circular orifice 25 is held against the sphericalsurface 20 so that the circular orifice 25 makes sealing contact withthe spherical surface 20, and the outer edge of the spring plate 24 isin sealing contact with the abutment face 26 of conduit 21, thuspreventing the passage of liquid 22. A plate 27 having a circular hole29 is assembled on to the outer face of spring plate 24 so that the hole29 is co-axial with orifice 25. A step or recess 30 in plate 27 providesa gap 28 between the spring plate 24 and plate 27, the assembly of thetwo plates being held in sealing contact with the abutment 26 byretaining member 33, which may be a crimped-on ring as shown.

Referring to FIG. 6, the liquid 22 is pressurised by the dispensingmeans (not shown), and forces plate 24 away from the spherical surface20, against the inherent bias provided by the fact that the plate 24 isa spring plate, to create the gap 32 between the circular orifice 25 andspherical surface 20. The size of the gap 32 is determined by the sizeof the gap 28 and by the diameter of the hole 29 in the plate 27, which,between them, determine the extent to which the spring plate 24 canflex. The liquid issues from the gap 32 as a thin circular sheet, theouter edge of which breaks into droplets as previously described. Theedge of the circular orifice 25 in spring plate 24 may have a chamfer 40as shown in FIG. 7, which may permit a wider spray angle than possiblewith a square-edged orifice. The spring plate 24 may have corrugations41 co-axial with the orifice 25 as shown in FIG. 8, which willfacilitate the flexing of the spring plate. When the pressure is removedfrom the liquid 22, the spring plate 24 returns to sealing contact withthe spherical surface 20.

In FIGS. 5 and 6 the spherical surface 20 is shown diagrammatically asbeing at the end of a rod, and means (not shown) would be required tosupport the rod with respect to the fluid discharge conduit 21. FIGS. 9and 10 show a modified embodiment in which there is a spherical surface20a formed on a disc 50 which is secured to, or integral witty, theinner wall of the conduit 21. The disc 50 is provided with at least oneport 51 through which liquid can pass from the interior of the conduit21 to the region immediately below the plate 24.

FIGS. 11 to 13 show a spray device incorporating an atomizing nozzleaccording to the present invention. It is intended for use as aninhalation device. It comprises a reservoir 60 of liquid 61. The liquid61 may, for example, consist of an aqueous suspension of a medicamentsuitable for treatment of a condition such as asthma. The lower end ofthe reservoir is defined by a piston 62 which is longitudinally slidablewithin the reservoir. Beneath the piston is a stopper 63 which has atleast one orifice 64 therein to permit air to enter the space beneaththe piston.

The upper end of the reservoir has a neck portion 65 to which a closuremember 66 is secured. A portion 67 of the closure member extends withinthe neck, and an O-ring seal 68 provides a seal between the neck portion65 and the portion 67. The closure member 66 has a passage 69therethrough and a tube 70 is secured in the upper portion of thispassage. The lower portion of the passage defines an orifice 71, abovewhich is a tapered portion defining a seat for a check valve ball 72.The ball is urged against the seat by a compression spring 73.

An outlet member 74 is mounted on the closure member 66 so as to bemovable with respect thereto. The outlet member 74 comprises a generallycylindrical part 75 the lower end of which engages over the closuremember 66. The part 75 is prevented from separating from the closuremember 66 by interengaging flanges 76 and 77 thereon. The outlet member74 further comprises an outlet spout 78 through which a user can inhalethrough his or her mouth. In the case of an inhaler for nasal use, thespout 78 would be replaced by an appropriate nasal outlet.

In the region of the junction between the cylindrical part 75 and theoutlet 78, the outlet member 74 has an inwardly extending wall 79 whichserves to retain an atomizing arrangement 80. This includes a block 81which has a hollow lower portion 82 which surrounds the upper end of thetube 70 and which is free to enter a cavity 83 in the upper end of theclosure member 66. The hollow portion 82 has an outwardly extendingflange 84 at its upper end, and a compression spring 85 is mountedbetween the flange and the closure member 66.

The interior of the hollow portion 82 communicates via a passage 86 withan atomizing nozzle 90 according to the invention. This is shown on alarger scale in FIG. 13. As can be seen there, it correspondssubstantially to what is shown in FIGS. 9 and 10, and comprises a springplate 91 which cooperates with a spherical surface 92 formed on a disc93. The disc 93 is provided with at least one port 94 therethrough.

In operation, the user places his or her mouth over the spoilt 78 andsqueezes the reservoir 60 and outlet member 74 together against theforce of the compression spring 85 to bring the device into the positionshown in FIG. 12. During this operation, the ball 72 prevents liquidleaving the reservoir 60 through the orifice 71, and the tube 70 acts asa piston to expel part of the liquid above the ball through the nozzle90 where it forms an atomised spray. The quantity of liquid expelled inthis way constitutes a metered dose, metering being effected by thestroke of the piston. The user inhales this spray. When the user ceasesto hold the reservoir 60 and outlet member 74 together, the spring 85forces them apart. This creates a suction effect within the tube 70which draws the ball 72 away from its seat and permits liquid to passfrom the reservoir through the orifice 71 to replenish what has justbeen dispensed through the nozzle 90. As the volume of liquid within thereservoir is reduced, the piston 62 slides upwardly under the force ofthe atmospheric pressure below it, air reaching the underside of thepiston through the port 64.

FIG. 14, shows another embodiment of spray device. The figure shows thedevice in the discharge position. In this embodiment, a valve of similardesign to that used as the atomizing nozzle is used also as a non-returninlet valve. FIG. 14 shows an actuator 101 sealingly located on a hollowstem 104 which is integral with a hollow piston 107. Piston 107 isslidingly located within the cylinder 115, the cylinder being formed asthe inner part of a pump body 108. The body is retained by a snap fit orother convenient method of retention in a closure 105, a gasket 106providing a seal between the stem 104 and the closure 105. Gasket 106 isfree to flex with axial displacement of the piston and stem, whilstmaintaining a seal. A plurality of cantilever springs 109, formedintegrally with piston 107, urges the piston in an outward direction byreacting against a conical surface 110 formed in the lower part of thepump body 108. The piston is prevented from coming out of the pump body108 by an abutment 116 closing on to the gasket 106 which is supportedby the inside of the closure 105.

The lower end of the pump body 108 contains a spherical surface 111. Aflexible diaphragm 112 with a circular hole therein is sealingly locatedin the pump body 108 so that the edge of the hole is in sealingengagement with the spherical surface 111. The combination of diaphragm112 and surface 111 acts as a normally closed non-return valve 120. Theextreme lower part of the pump body 108 terminates in a diameter adaptedto sealingly retain a dip tube 113. The conduit defined by the dip tube113 and extreme lower part of the pump body 108 is in communication withan annulus 119 formed between the spherical surface 111 and thediaphragm 112 via one or more ports 117. The actuator 101 has aspherical surface 103, and a flexible diaphragm 102 with a circular holetherein, the edge of which hole is in sealing engagement with thespherical surface 103. The diaphragm 102 is sealingly located by a snapfit or other convenient method within the actuator 101, and thecombination of diaphragm 102 and surface 103 acts as a combinednon-return valve and atomizing nozzle 121. The hollow stem 104 is incommunication with annulus 114 via a port 118.

In operation, the actuator is depressed and allowed to return severaltimes to prime the pump, the valves 120 and 121 cooperating to drawliquid from a reservoir (not shown) and to discharge the liquid from theatomizing nozzle.

FIG. 15 shows an atomizing nozzle in which, unlike those described sofar, a means is provided for enabling the gap through which the liquidpasses to be adjusted. The nozzle comprises a body 201 which has athreaded exterior to receive a threaded cap 202. The cap may be adjustedto alter a gap 203 formed between a face 204 of the cap and a flexiblediaphragm 205. In this way the discharge characteristics may be readilyadjusted; for example a spray may be adjusted from a fine to a coarsedroplet size.

The description "liquid" used in this specification includes solutions,suspensions and emulsions.

I claim:
 1. An atomizing nozzle for producing a spray of droplets from aliquid passing through the nozzle under pressure, which nozzle comprisesmeans defining the orifice; a closure member for the orifice, theorifice-defining means and closure member being relatively movable withrespect to one another between a first position in which the closuremember cooperates with the orifice to close the orifice and a secondposition in which the closure member is spaced from the orifice-definingmeans to define a gap therebetween, said orfice-defining means being aflexible diaphragm provided with at least one corrugation surroundingthe orifice, whereby to increase the flexibility of the diaphragm, and astop for limiting relative movement between the orifice-defining meansand the closure member to ensure that the width of the gap cannot exceedthat which would produce a fine spray.
 2. A nozzle according to claim 1,wherein said stop is arranged for engaging said closure member to effectthe limiting of relative movement between the orifice-defining means andthe closure membered, said orifice-defining means, said closure memberand said stop being configured and arranged relative to each other toensure that said closure member is aligned with said orifice duringengagement of said stop with said closure member so that said gapbetween said orifice-defining means and said closure member is uniformand annular.
 3. An atomizing nozzle for producing a spray of dropletsfrom a liquid passing through the nozzle under pressure, which nozzlecomprises an orifice, means defining the orifice; a closure member forthe orifice, the orifice-defining means and closure member beingrelatively movable with respect to one another between a first positionin which the closure member cooperates with the orifice to close theorifice and a second position in which the closure member is spaced fromthe orifice-defining means to define a gap therebetween, saidorifice-defining means being a flexible diaphragm; and a stop forlimiting relative movement between the orifice-defining means and theclosure member to ensure that a width of the gap cannot exceed thatwhich would produce a fine spray, the stop comprising an annular ringhaving a stop surface located adjacent to, but spaced from, thediaphragm.
 4. A nozzle according to claim 3, wherein the orifice iscircular.
 5. A nozzle according to claim 4, wherein the closure memberhas an at least partly spherical surface positioned to cooperate withthe orifice.
 6. A nozzle according to claim 5, wherein the closuremember is a spherical ball.
 7. A nozzle according to claim 3, whereinthe orifice-defining means and the closure member are relatively movablewith respect to one another under a force exerted by pressure of theliquid.
 8. A nozzle according to claim 3, wherein the orifice definingmeans has a chamfered peripheral surface, the direction of chamferingbeing such as to reduce the length of the said gap.
 9. A nozzleaccording to claim 3, wherein the width of the said gap is of the orderof 5 micrometers.
 10. A nozzle according to claim 3, wherein the valueof L/D, where L is the length of the said gap and D is the width of thesaid gap, is not more than
 1. 11. A nozzle according to claim 10,wherein the value of L/D is not more than 0.5.
 12. A nozzle according toclaim 3, wherein the orifice-defining means and the closure member arebiassed to the said first position.
 13. A nozzle according to claim 12,wherein the said bias is a resilient bias.
 14. A nozzle according toclaim 13, wherein the said resilient bias is provided by theorifice-defining means being resiliently movable.
 15. A nozzle accordingto claim 3, wherein said stop ensures that said gap is uniform and thatthe fine spray produced is substantially uniform in distribution aroundsaid gap and in droplet size.
 16. A nozzle according to claim 3, whereinsaid stop is arranged and configured to define an extent to which saidflexible diaphragm may flex so that an outer edge of a sheet of liquidemerging from said gap breaks into droplets.